A hybrid-electric or all-electric vehicle includes a traction battery constructed of multiple battery cells in series and/or parallel. The traction battery provides power for vehicle propulsion and accessory features. The traction battery typically operates at high voltages. Under normal conditions, a high-voltage system is designed to have a high resistance between the traction battery terminals and ground. However, it is possible during operation that the leakage resistance decreases for a number of reasons. Many high-voltage systems include circuitry to monitor and detect the presence of an abnormal leakage current within the traction battery.